Hydrophobic coating for ink jet printing heads

ABSTRACT

The invention provides inkjet print head which has an Anti-wetting Coating of a polymer material, which is produced with the utilization of at least one Compound (I) X a R b SiR 1   (4-a-b)  with X=hydrolyzable group, R=possibly substituted Alkyl, Aryl, Alkenyl, Alkylaryl or Arylalkyl, R 1 =organic remainder with at least one polymerizable group, a=to 3, b=0 to 2. In addition, a Process for the Manufacture of the Print Heads is made available, as well as a Means for the Coating of same.

The present invention concerns inkjet printheads withanti-wetting-coating. The term “anti-wetting”-coating signifies,vis-a-vis the ink, a hydrophobe coating, specifically a jet platecoating.

An essential pre-requisite for a clean print image of an inkjetoperating-based printer is a symmetrical droplet form, i.e. there mustbe no unilateral influence upon the ink when exiting from the printhead. Since inkjet print heads are customarily manufactured insandwich-type construction and may consist of highly differentmaterials, (silicon-wafer/channel-like structured polymer(PARAD)/Polyimide-Layer/alkaline earth glass) the print head, up to now,has usually been vaporized with a fluorine compound in order to producea uniform anti-wetting-layer at the ink jet exits. The vaporizationprocess is extremely costly and leads to unsatisfactory results.Furthermore, the face surface of the inkjet print head, which is roughas a result of sawing, must have been polished prior to vaporization,i.e. it must have been lapped, that is to say, smoothed out via costlyand time-consuming process.

Specifically with respect to the circumstance that disposable printheads have in the meantime come on the market, which are each timeexchanged together with the ink cartridge, the above describedvaporization process, including its prerequisites, proves too expensive.

It is, therefore, the object of the invention to discover ananti-wetting-coating material which adheres well to the substratematerial, and having hydrophobic properties with respect to the ink,which can be inexpensively applied and is cost-friendly.

Said object is solved by making available an Inkjet Print Head accordingto claim 1 and, in specifically beneficial fashion, according to theSub-claims 2 to 7.

Preference is given to the use of Compounds I as sole or principalcomponent for the manufacture of the polymer material.

The anti-wetting-coating of the present invention is suitable for eachtype of jet exit surfaces (for example jet plate, with sandwichconstruction, side shooter, edge shooter, back shooter). It is, amongothers, chemically inert vis-a-vis the different ink systems, because itdoes not swell upon contact with ink. Depending upon the ink system tobe employed, the wetting properties can readily be optimally adjusted oradapted by means of variation of the respective chemical groups.

The basic materials can be easily stored and are environmentallyfriendly.

By application of a material according to claim 1 as anti-wetting-layer,good adhesion is obtained with respect to the materials utilized for theheads; excellent compatibility with the thermal expansion of thelayer-bonding has the result that the applied layers will not chip orflake off, even after being rejected to stress over a longer period oftime. Wetting angles relative to water are achieved in the range of 80°to more than 90°, and in some cases up to more than 100°. Surprisingly,it was also discovered that with Inkjet Print Heads coated according tothe invention, the roughness of the face surface due to wafer sawing isplanarized. There also exists capability of pinhole-free application.

Specifically, via a process according to claim 12, there is guarantee,in particularly beneficial manner, that the channels themselves are notpasted up with the coating.

Polymer materials as defined in claim 1, belong to a material categoryof the so called ORMOCERS (ORganically MOdified CERamics). They may beranked among the inorganic and organic polymers. Production takes placestarting from alkoxides of silicon, and possibly, as supplement to othermetals, which are totally or partially modified by organicallypolymerizable substituted groups. Via hydrolysis and condensation, theinorganic part of the network is formed, via polymerization,polyaddition or other organic coupling reactions the organic part (ofreactive organic substituted groups).

The following systems have proven themselves as particularly suitablefor use as polymer material for anti-wetting-coating.

TABLE 1 G-(Mol-%) P(Mol-%) 2(Mol-%) M(Mol-%) T(Mol-%) 30-40 — 10-2030-40 0-5 — 70-90 — 15-25 — — 80-95 —  5-15 — — 65-75 — 20-40 — — 35-4525-35 20-40 — — 50-70 25-35  5-15 — G = Glycidoxypropl-trimethoxysilane;P = Phenyl-trimethoxysilane; P2 = Diphenyl-silandiol; M =Methacryl-oxypropyl-trimethoxysilane; T = Tetra-ethoxy-silane.

The preferred manufacturing method for the material is that the desiredsilanes are first mixed with any other perhaps required additives (forexample network builders or modifying substances), and, if required,under calefaction, hydrolyzed by addition of water. Addition of watercan be done slowly, so that the system is initially supplied withsub-stoichiometrical quantities.

In one embodiment of the invention, the systems also contain one aminocomponent, for example N-methyldiethanolamine (NMDA) and/ordiethylenetriamine (DETA). This can act as an accelerator. The twoaforementioned substances are preferably employed at a ratio ofapproximately 1:1 and in a volume of approximately 0.5-2, preferablyapproximately 1 volume-% relative to undiluted lacquer.

The liquid lacquer, produced as described above, is brought, whererequired, to a desired solid matter contents and can subsequently beapplied as such on the print head or, as is preferred, in combinationwith a solvent (for example ethanol, acetone, propylacetate or similar).The preferred application procedure is spraying. Alternativepossibilities are, for example, spin-coating, roll-application or tamponprint. Additional possibilities are off-set print, application by brushor immersion application. The mode of application is usually selected insuch manner that optimum adaptation is possible with respect to headgeometry and head production sequence. After the application, thematerial is hardened (organically polymerized). This can be done forexample via photo-chemical and/or thermal method, whereby, of course,for photo-chemical hardening photo-initiators need to be added to thelacquer, prior to application. In case of spray application, one can,for example, operate with a spray precompression of 0.5 to 2 bar, forexample (jet cross sections: 0.1 to 0.3 mm). Spray distance can, forexample, be 3 to 10 cm, specifically approximately 6 cm. In order toprevent any clogging of the fine inkjet exit apertures, Nitrogen can bepassed through each print head, for example with a counterpre-compression of 0.5 bar.

Suitable photoinitiators are known to a person skilled in the art. Forexample, radically-ionic initiators can be employed such as Cyracure UVI6974 by Union Carbide. Adding amines such as N-methyidiethanolamineand/or Diethylenetriamine shortly before application is particularlybeneficial, even with utilization of radical photostarters such as forexample Quantacure ITX (Rahn Chemie). The photo-initiators can, forexample, be added in amounts of 1-5 mass-%, preferably approximately 2mass-%, relative to the undiluted lacquer.

The solid matter contents of the lacquer produced in the initial phaseis variable. For example, it can amount to between 30 to 80%. Theadjustment is preferably made via rotary incorporation. Subsequentlydilution with solvents is also variable and depends upon several to beselected factors, for example upon the type of application. The lacquercan, for example, be brought to a final solid matter contents ofapproximately 5 to 30% by means of solvents.

Excellent layer qualities are obtained with a lacquer which was broughtby means of rotary incorporation to approximately 60 to 70% by weight ofsolid matter contents and was then diluted by solvents (for examplePropylacetate) to a solid matter contents of approximately 10% byweight.

According to the invention, it is also possible to apply a secondhydrophobic layer, for example of a fluorized hydrolyzed silane. Thus, aPerfluoralkl-triethoxysilane may be used.

Preferably, both these layers are jointly hardened (thermally and/orphoto-chemically). Furthermore, the anti-wetting-layer according to theinvention can be developed from several layers of the material accordingto the invention, which are applied successively and are of identical ordifferent compositions.

EXAMPLES

1. Basic Compounds for the Lacquers

System G-(Mol-%) P(Mol-%) 2(Mol-%) M(Mol-%) T(Mol-%) GMP2T 38.6 — 18.938.6 3.9 PM82 — 80 — 20 — PM91 — 90 — 10 — PM73 — 70 — 30 — PP2M433 — 4030 30 — PP2M631 — 60 30 10 —

2 Lacquer Synthesis

2.1 Synthesis of GMP2T

Starter Compounds

1. 0.4 mol g-Glycidopropyltrimethoxysilane (=38.6 mol-%)

2. 0.4 mol g-Methacryloxypropyltrimethoxysilane (=38.6 mol-%)

3. 0.2 mol Diphenylsilandiol (=18.9 mol-%)

4. 0.04 mol Tetraethoxysilane (=3.9 mol-%)

5. 2.37 mol water

Components 1-4 are introduced and stirred at room temperature for 18hours. Subsequently, the suspension is heated within 90 minutes toapproximately 70° C. After the suspension has become clarified, ¼ of theamount of water is added while firing is maintained. In time intervalsof approximately 20 minutes, the remaining water is added (in amounts of¼ each). After all the water has been added, stirring is continued forone hour at 70° C. Subsequently, firing is eliminated and after coolingdown, the lacquer is ready to use.

2.2 The other lacquers are produced similarly to GMP2T.

3. Manufacture of the Anti-wetting-coating on the Inkjet Printer.

3.1 Manufacture of the material to be applied.

Lacquers having the above described compositions are adjusted by rotaryincorporation to a solid matter contents of 66.5% by weight and dilutedwith ethanol or propylacetate to 5-40% by weight of solid mattercontents.

3.2 Application of Coating on the Print head.

With an air brush (type Aerostar 105 by Messrs. Fischer) the lacquer issprayed with a spray pressure of 0.5 or 2.0 bar (et cross section 0.2mm) at a spraying distance of approximately 6 cm onto the front sides ofthe fully assembled inkjet print heads. Nitrogen is passed through eachhead with a reverse supply pressure of 0.5 bar. Subsequently, allsystems are photo-chemically hardened (initiator: Cyracure UVI 6974 byUnion Carbide).

One portion of the lacquers additionally contains N-Methyldiethanolamine(NMDA) and Diethylenetriamine (DETA) at a ratio of 1:1.

Exposure time is 15 seconds. Subsequently, as is apparent from Table 3,some of the systems are thermally after-baked.

4. Ink Storage Test (70° C.; 150 hours; commercially availableink-water/alcohol basis) Specimens for the ink storage tests areproduced under the following conditions: Solid matter percentage in thespray lacquer: approximately 7% by weight; Solvent: Propylacetate; Photoinitiator: Cyracure UVI 6974 (3% by mass relative to undiluted lacquer);Amines: NMDA +DETA (1:1; 1% by mass relative to undiluted lacquer);Hardening: 60 seconds with 500 W (Loctite).

The following adhesion values (=GT) and wetting angles (vis-a-vis water)are ascertained prior to (=index v) and after (=index n) the ink storagetest.

TABLE 3 System therm. hardng. Substrate GT_(v) GT_(n) angle_(v)angle_(n) GMP2T  1 h/80° C. Glass 0 0 79° 78° ″ Wafer 0 0 ″ Parad   0.5  0.5 ″ Vacrel 0   0.5 GMP2T^(a) 16 h/80° C. Glass   0.5   0.5 74° 66° ″Wafer 0 0 ″ Parad 0 0 ″ Vacrel 0    0.5^(b) PM82 ″ Glass 0 5 80° 61° ″Wafer   0.5 5 ″ Parad 0 5 ″ Vacrel 0 5 PM82^(a) 16 h/80° C. Glass   0.5  0.5 ″ Wafer 0 0 ″ Parad   0.5   0.5 ″ Vacrel 0  5^(b) PM91^(a) 16h/80° C. Glass 1 1 77° 42° ″ Wafer   0.5   1.5 ″ Parad 1   1.5 ″ Vacrel  0.5  4^(b) PM73 ″ Glass 0 0 75° 70° ″ Wafer 0 0 ″ Parad 0   0.5 ″Vacrel 1 1 PM73^(a) 16 h/80° C. Glass 1 1 72° 91° ″ Wafer 1 1 ″ Parad 11 ″ Vacrel 1  —^(c) PP2M433  1 h/80° C. Glass 0 0 78° 79° ″ Wafer 0 0 ″Parad   0.5   0.5 ″ Vacrel 0 0 PP2M433^(a) 16 h/80° C. Glass 1 1 82° 76°″ Wafer 1 1 ″ Parad 1 1 ″ Vacrel 1  1^(b) PP2M631  1 h/80° C. Glass 0 079° 73° ″ Wafer 0 0 ″ Parad 2 2 ″ Vacrel 2 2 ^(a)165 hours ink storageinstead of 150 hours ^(b)Adhesion problem Vacrel Wafer (partialseparation of vacrel) ^(c)Vacrel separated from wafer, thereforeadhesion determination no longer possible.

System GMP2T shows the best adhesion values before and after the inkstorage test. System PP2M433 also provides comparably satisfactoryresults, and likewise has a comparably high wetting angle (if not evensomewhat higher). System PM73 has the greatest hardness and thusprobably also highest smearing resistance. It also has satisfactoryadhesion with respect to the different substrates.

Best wetting angles (up to more than 100° C.) are obtained withtwo-layer systems, in which the second layer is formed by afluor-silane.

The obtained surface thickness of the anti-wetting coating isapproximately 5 to 30μ.

Another, for the application essential property of the systems is theirplanarization capacity of rough surfaces. This makes possible the use ofSi-components which have only been sawed—in other words, thetime-consuming and thus cost-intensive lapping process can be eliminatedin the manufacture of the Inkjet Print Heads.

Having thus described the invention, we now claim:
 1. Inkjet Print Head,characterized in that it has an Anti-wetting Coating of polymermaterial, said Anti-wetting coating is formed in at least two layers,wherein an outer layer consists of perfluoroalkyltrialkoxysilane orcontains said perfluoroalkyltrialkoxysilane, said polymer material ismanufactured by utilization of at least one compound I X_(a)R_(b)SiR¹_((4-a-b))  I With X=hydrolyzable group R=optionally, substituted alkyl,aryl, alkenyl alkylaryl or arylalkyl, R¹=organic remainder with at leastone polymerizable group, a=1 to 3 b=0 to
 2. 2. Inkjet Print Headaccording to claim 1, characterized in that the Compound I is selectedamong alkytrialkoxysilanes, aryltriakoxysilanes, diarylkoxysilanes aswell as hydrolysis products of these silanes.
 3. Inkjet Print Headaccording to claim 1, characterized in that the polymer material ismanufactured with utilization of at least one compound from the groupGlycidoxypropyltrimethoxysilane, Phenyltrimethoxysilane,Diphenylsilandiol and Methacryloxypropyltrimethoxysilane.
 4. InkjetPrint Head according to claim 3, wherein the polymer material ismanufactured with utilization of Glycidoxypropyltrimethoxysilane,Methacryloxypropyltrimethoxysilane, Diphenylsilandiol andTetraethoxysilane.
 5. Inkjet Print Head according to claim 1,characterized in that the Anti-wetting Coating has a thickness rangingfrom 5 to 50μ.
 6. Process for the manufacture of anti-wetting-coatedInkjet Print Heads comprising forming a polymer material from at leastone compound X_(a)R_(b)SiR¹ _((4-a-b))  I With X=hydrolyzable groupR=optionally, substituted Alkyl, Aryl, Alkenyl Alkylaryl or Arylalkyl,R¹=organic remainder with at least one polymerizable group, a=1 to 3 b=0to 2, and spraying said polymer material onto the Inkjet Print Headwhile an inert gas is counter-conducted through inkjet openings. 7.Process according to claim 6, characterized in that the material, inform of lacquer from pre-condensed starter compound(s) through additionof water, is optionally applied, with a solvent, onto the Inkjet PrintHead and subsequently finish-cured photochemically and/or thermally. 8.Process according to claim 6, characterized in that the material issprayed on optionally with a solvent.
 9. Process according claim 6,characterized in that Propylacetate is used as solvent.
 10. AnAnti-wetting Coating for Inkjet Print Heads, said Anti-wetting coatingcomprising a polymer material, said Anti-wetting coating being formed inat least two layers, wherein an outer layer consists ofperfluoroalkyltrialkoxysilane or contains perfluoroalkyltrialkoxysilane,and said polymer material is produced from at least one Compound IX_(a)R_(b)SiR¹ _((4-a-b))  I With X=hydrolyzable group R=optionally,substituted Alkyl, Aryl, Alkenyl Alkylaryl or Arylalkyl, R¹=organicremainder with at least one polymerizable group, a=1 to 3 b=0 to
 2. 11.An Anti-wetting Coating for Inkjet Print Heads according to claim 10,characterized in that the Compound I is selected from amongAlkyltrialkoxysilanes, Aryltrialkoxysilanes, Diaryldialkoxysilanes, aswell as Hydrolysis Products of these Silanes.
 12. An Anti-wettingCoating for Inkjet Print Heads according to claim 10, characterized inthat the polymer material is produced from a compound selected from thegroup consisting of Glycidoxypropyltrimethoxysilane,Phenyltrimethoxysilane, Diphenylsilandiol andMethacryloxypropyltrimethoxysilane and mixtures thereof.
 13. AnAnti-wetting Coating for Inkjet Print Heads according to claim 10wherein said Anti-wetting coating is deposited directly adjacent saidprint head.